Common Name: Kalm's St. John's wort
Type: Broadleaf evergreen
Zone: 4 to 7
Height: 2.00 to 3.00 feet
Spread: 2.00 to 3.00 feet
Bloom Time: July to August
Bloom Description: Yellow
Sun: Full sun to part shade
Suggested Use: Hedge
Other: Winter Interest
Easily grown in average, medium, well-drained soils in full sun to part shade. Prefers moist, rich, sandy loams. Tolerates some drought.
Hypericum kalmianum, often commonly called Kalm St. Johns wort, is a evergreen shrub or subshrub with upright branching that typically grows in a dense mound to 2-3’ tall. It is native to the Great Lakes region where it typically occurs in rocky to sandy soils, ranging from relatively dry open woods to moist lakeshore areas. It features narrow, linear-oblong, bluish-green leaves (to 2” long) in pairs and 1.5-inch diameter, 5-petaled, golden yellow flowers in cymes in mid to late summer (July-August). Each flower has five styles and a distinctive boss of yellow stamens. Flowers give way to beaked, oval, brown seed capsules that mature in fall and often persist on the shrub until spring. Leaves are dotted with tiny glands. ‘Ames’ was developed at Iowa State University, and reportedly has better winter hardiness than the species. Genus name honors Peter Kalm, a student of Linnaeus, who reportedly discovered the species plant in the wild in North America in the mid-1700s.
No serious insect or disease problems.
Low hedge. Shrub borders. Wood margins, rocky slopes, wild gardens, naturalized areas or pond peripheries.